After the oil crisis and during the past three decades, biopolymers produced from biomass and having properties suitable for use as plastics, hence called as bioplastics, have gained a lot of interest as renewable alternative to petroleum based plastics. Among the several different types of bioplastics are polyhydroxyalkanoates (PHAs) that belong to the polyester class of polymers. Many bacterial and archaeal strains can accumulate PHA granules as intracellular carbon and energy reserves.
Poly(3-hydroxybutyrate), (PHB), is a homopolymer and is the most common type of PHA produced by microorganisms. Several microbial strains are also able to produce other PHA homopolymers or copolymers with varying monomer composition such as poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV), poly(hydroxybutyrate-co-hydroxyhexanoate) (PHBHx), poly(hydroxyoctanoate-co-hydroxyhexanoate) (PHOHx), etc.
PHAs are of interest as bio-derived and biodegradable plastics and have properties similar to the widely used fossil based plastics, polyethylene and polypropylene. Examples of properties may be thermoplasticity, good resistance to moisture, aroma barrier properties, etc. Also, the possibility to produce PHAs with different properties by varying the monomer composition, using different renewable carbon sources, and their complete biodegradability upon being decomposed in soil, make PHAs highly interesting substitutes for conventional plastics. Moreover, PHAs show great biocompatibility in different pharmaceutical and medicinal applications, in addition to their promising industrial and agricultural applications.
Polylactic acid or polylactide (PLA) is also a biodegradable aliphatic bioplastic derived from renewable resources, such as corn starch, tapioca roots, chips or starch, or sugarcane. PLA, like PHA, belong to the polyester class. Synthesis of PLA by recombinant bacteria has also been reported.
In WO14032633 a method for producing polyhydroxyalkanoates from oil substrate is disclosed. Further, in WO12149162 production of polyhydroxyalkanoate with genetically engineered microbes is disclosed.
There are however several drawbacks to the processes and methods known today, and e.g. described in these documents. Processes for production of PHA bioplastics involve methods of extracting the produced bioplastic material from the microbial cells producing said bioplastic. Today such methods involve various chemicals as part of the process. Chemicals that could be used to extract the bioplastic from the cells may be chosen from organic solvents, detergents, acid, alkali, or hypochlorite. The use of different types of chemicals in the production of bioplastics is both costly and not desirable due to their high environmental impact.
Attempts have been made to circumvent these drawbacks. WO08065749 and WO11145683 disclose methods for producing natural polymeric substances for molding of a biodegradable material. In the documents the method of extraction utilizes a time consuming drying and grinding step providing an end product of low purity.
There is a need to provide bioplastics in more environment-friendly and cost efficient ways in order to be competitive with the petrochemically derived plastics.
On the other hand, PHAs are regarded to be a novel renewable source for enatiomerically pure chemicals via depolymerization of PHAs into its monomeric composition, R-3-hydroxyalkanoic acids (R-3-HAs). Because of the interesting industrial and medical applications of R-3-HAs, different chemical and biological depolymerization methods are being investigated to achieve an economic and easy-to-apply process for R-3HA production from PHA.